Manufacture of mixed cellulose esters



Patented Dec. 5, 1933 UNITED STA Camille Dreyfus, New York, N. Y., andGeorge W. Miles, Boston, Mass, assignors to Celanese Corporation ofAmerica, a corporation of Delaware i No Drawing. Application October 26,1928 Serial No. 315,356

11 Claims. (01. 2601-101) ployed catalysts or by using only very smallamounts of such catalysts.

Still another object or" our invention is to devise a process for makingmixed inorganic-organic esters of cellulose inone operation.

Still another object of our invention is to devise a process for makingmixed esters of cellulose wherein the esterifying agents em ployed actas dehydrating agents, the one for the other. a

Still another object of our invention is to produce mixedcellulosenitrate and acetatewhich is esterified to a greater degree thanhas heretofore been considered possible.

Still another object of our invention is to produce mixednitrate-acetate cellulose which is very stable even when the nitrogencontent of such compound is very high; Other objects and advantages willappear from the following detailed description.

Heretofore in producing mixed esters .of cellulose it has been thoughtnecessary to first esterify the cellulose with one esterifying agent andto replace part of these ester groups by treatment with anotheresterifying medium. In other in- I stances where cellulose esterproducts containing more than one species of acid radicals were de-,sired, these were obtained by physically mixing the different celluloseesters in the desired proportions. Theproducts of the latter processeswere not true chemical compounds but were in fact merely mixtures of thedifferent ingredients. We'have found that it is unnecessary to followthese long and expensive procedures in order to obtain mixed esters ofcellulose. We havediscovered a process whereby two different species ofester groups can be introduced into the cellulose molecule in'oneoperation. Thismakes it possible to obtain variousmixed cellulose estersat a greatly reduced cost] and -in a very much shorter time than isrequired under the present ractice. I

)Our invention also enables'us to; procure mixed esters containing thediiierent ester groups in any desired ratio, one to another. We havealso been "able to-obtain, by virtue of our process, a

- much 'higher degree of- 'esterification thanha's heretofore beenobtainable or considered possible. Our invention is of particular valuein the manufacture of mixed nitrate and acetate of cellulose, since itpermits the nitration and acetylation of'the cellulose in one operationand in a single bath. In addition to the savingof time, this improvementhasother beneficial results. Nitrate-acetates of cellulose have beenobtained which have a high nitrogen contentfbut are nevertheless verystable and which at the same time possess the valuable properties of therespective esters.

-We have also discovered that it is possible to make these mixednitrate-acetates of cellulose without the use of "catalysts such as areusually employed in the manufacture of cellulose esters. We may dispensewith the use of sulphuric acid as a c'atalystgthereby avoidingthe-formation of the sulpho compounds to which the unstable propertiesof nitro cellulose are usually attributed.

The cellulosic material treate din accordance with our process may beany suitable cellulose or its derivatives. It may be cotton,cottonlinters,

' wood pulp or other forms of cellulose. The cellu- TESI PATENT OFFICElosic material may be pretreated in any. known manner in order topromote and facilitate its cellulosic material, such as cotton linters,with acetic anhydride, glacial acetic acid and fuming nitric acid at orbelow, preferably below, room temperatures. can beeifected in theabsence of glacial acetic acid. Also phosphoric acid (H3PO4 or HPOs) canbe added to the esterifying bath with beneficial results especiallywhere it is desired to esterify the cellulose without the use of aceticanhydride. In some instances, small amounts of sulphuric acid may beused as a catalyst for the reaction. I

Although this description is largely. concerned with the manufacture ofnitrate-acetate of cellulose, this invention is not tobe considered aslimited thereto. Other mixed esters can also be madeby our process, forexample, nitrate proe pionate of cellulose, nitrate butyrate ofcellulose, etc. .In like manner the amounts of reagents given in theexamples which follow are not limitative. The amounts of the variousreagents will vary with the final product which is desired.

These end products can be of such infinite variety Where desired theesterification.

to utilize in order to obtain the various producta The products obtainedby the process herein disclosed have an unlimited number of applicationsin the arts and in industry. Thus the products containing acomparatively high nitrogen content can be employed. in the explosivefield. The acetyl content of the mixed ester has only a beneficialeffect on the compound, increasing its stability without having anyappreciable deterrent effect on its combustibility. Such high nitrogencontent esters can also be used in the plastic arts where heretoforeonly low nitrogen content nitro cellulose could be employed. This is dueto the fact that although the combustibility of the mixed ester has notbeen reduced, its stability during processing has been materiallyimproved.

These mixed esters, due to their excellent properties, therefore are ofgreat utility in all branches of theplastic art. They also furnishexcellent bases for lacquers, varnishes and films. They can also be usedin manufacturing laminated glass. In short these mixed esters affordexcellent substitutes for the respective individual esters, usuallyexcelling the single esters in their adaptability. t

For obtaining greater reactivity of the cellulosic material and thusinreasing the rate of the esterification process and also to obtain amixed cellulose ester of higher clarity, we prefer first to subject thecelluloseto a preliminary treat ment which may include either apretreatment process or a prehydrolysis process or both a pretreatmentor a prehydrolysis process.

The pretreatment process comprises the treatment of the, cellulosicmaterial with a relatively small proportion of a lower fatty acid suchas propionic acid, formic acid or acetic acid, and in the presence or inthe absence of a small amount of a catalyst such as sulphuric acid. Thepropionic, formic or acetic acid may be applied to the cellulosicmaterial in any suitable manner either in the form of a liquid, or inthe form of a vapor.

As illustrations of a few methods of carrying out our invention, thefollowing examples are given. The parts as indicated are by weightunless otherwise indicated.

Example I 1100 parts of acetic anhydride are mixed with about 400 partsof fuming nitric acid, both liquids Example II 100 parts of cellulose(cotton linters) are introduced into approximately 1000 parts of glacialacetic acid and allowed to stand about 15 hours at room temperatures.The mass is then cooled with ice water and to this cool mass is added acold mixture of about 400 parts of fuming nitric acid, 400 parts ofacetic anhydride and 400 parts of glacial acetic acid. The mass is wellstirred,

cooled and allowed to stand about 16 hours at room temperatures. Thereaction mass is then subjected to the hereinafter described secondarytreatment. The final product on analysis showed a nitrogen content of7.96% and an acetyl value of 16.52%.

Example III Example IV 1100 parts of 95% H3PO4 are mixed with 450 partsof fuming nitric acid and cooled in ice water. To this cool mixture isadded 325 parts of acetic anhydride and parts of cotton linters, and themixture kept in ice water for about two hours. The reaction mixture isthen allowed to stand for about 18 hours in a water bath at about 20 C.The mass was then subjected to an after treatment as hereinafterdescribed. Upon analysis the final product was found to have a nitrogenvalue of 13.39% and an acetyl value of 25.52%.

Example V 100 parts of cellulose are introduced into 630 parts ofglacial acetic acid and allowed to stand for one hour in ice water. 60parts of fuming nitric acid in 150 parts of cold glacial acetic acid isthen added and finally 325 parts of acetic anhydride containing 10 partsof sulphuric acid are introduced into the mixture. The reaction mixturewas allowed to stand for about 16 hours after which time it wassubjected to thehereinafter described secondary treatment. The finalproduct had a nitrogen content of 5.59% ,and an acetyl value of 42.0%. I

Example VI 100 parts of cotton linters are put in a bath of 630 parts ofglacial acetic acid and allowed to stand over night. This is then cooledwith ice water and to it is added about 380 parts of acetic anhydridecontaining 40 parts of sulphuric acid. There is then added 100 parts ofcold glacial acetic acid containing 60 parts of fuming nitric acid. Thereaction was completed in half an hour and the product washed. Onanalysis it showed a nitrogen content of 3.75% and an acetyl value of34.44%.

It is to be understood that the above examples and the foregoingdetailed description are given merely by way of illustration and ourinvention is not to be considered as limited thereto. Many variationsfrom the above specific examples may be made without departing from thespirit of our invention.

It will be seen from the above examples that the cellulose is esterifiedto a remarkably high degree-in fact to a degree hitherto unattainableand considered impossible. The nitrogen and acetyl figures given arebased on the esterified cellulose and a nitrogen value of 13.79%, forexample, is in fact comparable to a nitrogen content of between 15 and16% in a straight nitrocellulose. The same is also true of the acetyl;

value.

is the fact that the esterifying agents also act as dehydrating agents.The acetic anhydride acts as a dehydrating agent for the nitration andthe fuming nitric acid acts as a dehydrating agent for the acetylation.

The reaction masses resulting from the above examples are then subjectedto an after-treatment. The masses are tested for free anhydride and thelatter is then hydrolized by the addition of the requisite amount ofwater. A slight excess of water is added and the mass allowed to ripenfor a period of twenty four hours at about to C. A sample taken from themass at the end of this time is precipitated by water, washed free ofacid and dried and should show the solubility in acetone desired. Whenthis test shows the proper solubility in acetone or other solvent usedas guide, the mass proper is similarly precipitated. and washed untilfree of acid.

The precipitated product is then placed in about twenty times its weightof water containing less than .05% of sulphuric acid and boiled for aperiod of four hours or until a sample of the above materiahwhen dried,shows the desired solubility in acetone, ethyl acetate, etc. Thistreatment with boiling water containing a trace of mineral acid servesthe double purpose of splitting up the sulfo esters of cellulose formedduring the reaction when sulphuric acid is used as catalyst, thusincreasing the thermo stability of the product, and at the same time,completing the hydrolysis of the product, the main portion of which isaccomplished during the ripening process, so that the product is solublein the solvents desired, which comprises those enumerated above.

Having described our invention what we claim and desire to secure byLetters Patent is:

1. Method of producing mixed nitrate-acetate of cellulose whichcomprises treating material consisting substantially of cellulose withacetic anhydride and fuming nitric acid in one bath.

2. Method of producing mixed nitrate-acetate of cellulose whichcomprises treating material consisting substantially of cellulose withacetic anhydride, glacial acetic acid and fuming nitric acid in onebath.

3. Method of producing mixed nitrate-acetate of cellulose whichcomprises treating material consisting substantially of cellulose withacetic anhydride, phosphoric acid and fuming nitric acid in one bath.

4. Method of preparing mixed nitrate-acetate of cellulose whichcomprises treating material consisting substantially of cellulose withacetic anhydride and fuming nitric acid simultaneously in one bathbetween about 0 C. and room tem-- peratures. v

5. Method of preparing mixed nitrate-acetate of cellulose whichcomprises treating material consisting substantially of cellulose withacetic anhydride, glacial acetic acid and fuming nitric acidsimultaneously in one bath between about 0 C. and room temperaturesuntil a nitrogen content of over 3.75% is obtained.

6. Method of producing mixed nitrate-acetate of cellulose whichcomprises pretreating material consisting substantially of celluloseWith a lower aliphatic acid and then treating the pretreated materialwith acetic anhydride and fumingnitric acid in one bath.

7. Method of producing mixed nitrate-acetate of cellulose whichcomprises pretreating material consisting substantially of cellulosewith a relatively small proportion of acetic acid and then treating thepretreated material with acetic anhydride and fuming nitric acid in onebath.

- 8. Mixed nitrate-acetate of'cellulose whose nitrate and acetateradicles are introduced in the cellulose molecule simultaneously, saidnitrateacetate of cellulose having a nitrogen content of at least13.28%.

9. Mixed nitrate-acetate of cellulose whose nitrate and acetateradiclesare introduced in the cellulose molecule simultaneously, saidnitrateacetate of cellulose having a nitrogen content of at least13.28%, being free of catalysts and having a high degree of stabilityand combustibility.

10. Mixed nitrate-acetate of cellulose whose nitrate and acetateradicals are introduced in the cellulose molecule simultaneously, saidhitrate-acetate of cellulose having a nitrogen content of 13.79% and anacetyl value of 32.34%.

11. Mixed nitrate-acetate of cellulose whose nitrate and acetateradicals are introduced in the cellulose molecule simultaneously, saidnitrate-acetate of cellulose having a nitrogen content of 13.79% and anacetyl value of 32.34%, being free of catalyst and having a high degreeof stability and combustibility.

CAMILLE DREYFTUS. GEORGE W. MILES.

